Lead extrusion



Feb. 22, 1949. w. K. FREEMAN 2,462,313

LEAD EXTRUS ION Filed March 4, 1946 :5 Sheets-Sheet 1 INVENTOR lt/4L7ER K FRE MAN ATTORNEYS Feb. 22, 1949. w. K. FREEMAN 2,462,313

LEAD EXTRUSION Filed March 4, 1946 I 5 Sheets-Sheet 2 INVENTOR WA L TER h. FREEMAN BY 75%, M, M @fiM ATTOR N EY5 Feb. 22, 1949. w. K. FI-REEMAN LEAD EXTRUSION 3 Sheets-Sheet 3 Filed March 4, 1946 INVENTOR M I v H 5 WW mo mwm R, M M

Patented Feb. 22, 1949 umao @FFICE LEAD EXTRUSION Application March 4, 1946, Serial No. 651, 729

2 Claims.

This invention relates to improvements in lead extrusion and, more particularly, to improvements in the charging of lead to a lead extrusion press.

In the extrusion of lead, as in the manufacture of lead pipe and particularly in the extrusion of a lead sheath about an electric cable, it is of utmost importance that the extruded lead be of uniformly high quality. In lead sheaths, for example, the slightest discontinuity in the sheath is a potential source of failure in service. The problem of producing extruded lead of uniform quality from a single charge in an extrusion press has been mastered. But a serious problem has remained, the maintenance of continuously uniform quality as successive charges are made to an extrusion press. The discontinuity is due largel to the fact that the surface of the lead against which the extrusion ram presses becomes somewhat oxidized. In addition to such oxidation, the surface of the hot lead in the press is frequently contaminated with the oil, soap or other lubricant used for lubricating the ram.

The better the lubricating qualities of the oil, for example, the more tenaciously the oil adheres to the surface of the lead.

One method of combating this oxidation of the hot lead in the press during recharging has been to maintain a non-oxidizing atmosphere in the press cylinder while the necessary. charge of molten lead is being poured into the press cylinder. A different approach to the solution of this problem has been to pour the molten lead into the press cylinder through an extension secured to the spout of the molten lead kettle with this extension delivering the molten lead directly to the surface of the lead in the bottom of the press cylinder. The flow of molten lead against the surface of the previous charge of lead tends to melt a portion of this surface and thereby loosen the impurities which then tend to float to the surface of the molten charge. A combination of this method of charging molten lead and of maintaining a non-oxidizing atmosphere in the press cylinder has also been'used. However, none of the methods proposed or used heretofore has completely removed all impurities to such an extent that the extruded metal is free of these impurities. As a result, non-uniformities in quality of the extruded lead have appeared.

The primary object of the present invention is to eliminate impurities between successive charges in such lead extrusion processes. This result is accomplished in accordance with the present invention by mechanicall loosening and removing the surface of the lead remaining in the extrusion press, and then introducing into the press a new charge of lead. A non-oxidizing or reducing atmosphere may be maintained with advantage over the charge of lead in the press.

When the lead is charged in the solid form, one

surface of the solid charge is advantageously provided with a substantially non-oxidized clean surface, as by providing it with a freshly cut surface, and the charge is introduced into the press with this surface brought into contact with the cleaned surface of the lead remaining in the press. A feature of the invention is the removal of the surface of the lead already present in the press by scraping or cutting it with an appropriate cutter. A cutter which has been developed for this purpose in accordance with the invention comprises a rotatable member provided with a substantially radially disposed cutting blade. The blade is adapted, upon rotation of the rotatable member, to cut away'the surface of the body of lead in the press so as to loosen and remove the impurities in or on the surface. The rotatable member is advantageously disc-shaped and is provided with a radial opening or slot extending from about the center of the disc to the periphery of the disc. The cutting blade is mounted within this slot with the cutting blade extending beyond the lower surface of the disc and advantageously sloping backwardly and upwardly with respect to its direction of movement so as to cut away thesurface of a lead charge and to discharge it onto the upper surface of the disc.

The invention will be further described in conjunction with the accompanying drawings, in which:

Fig. l is a schematic representation of the position of a charge of lead in a press at the end of the ram stroke;

Fig. 2 is a cross-section of the lead sheath produced at the extrusion stage shown in Fig. 1;

Fig. 3 is a schematic representation of the relative positions of old and new charges of lead after a portion of the new charge has been extruded in accordance with conventional extrusion practice;

Fig. 4 is a cross-section of the lead sheath produced at the extrusion stage shown in Fig. 3;

Fig. 5 is a schematic representation of the relative positions ofold and new charges of lead after a major portion of the new charge has been extruded by conventional extrusion practice;

Fig. 6 is a. cross-section of the lead sheath produced at the extrusion stage shown in Fig. 5;

Fig. 7 is a schematic representation-of the relative positions of old and new charge immediately after pouring a new charge by the extension spout practice;

Fig. 8 is a schematic representation of the flow of the charge shown in Fig. 'I after a portion of the new charge has been extruded;

Fig. 9 is a cross-section of lead sheath produced at an extrusion stage subsequent to that shown in Fig. 8;

Fig. 10 is a top view of the cutter of the invention; and

Fig. 11 is a sectional side view showing the cutter in place within the cylinder of a lead extrusion press.

The schematic representations shown in Figs. 1, 3 and 5 illustrate the flow of lead at different stages in conventional extrusion practice wherein a new charge of lead is poured directly onto the surface of the old or previous charge remaining in a press cylinder ll. At the end of the ram stroke as shown in Fig. 1, a layer of impurities 12, such as oxides, lubricant, and the like, is left on the surface of the old charge l3 below the ram M. The lead sheath produced at this extrusion stage, as shown in Fig. 2, is composed essentially of the lead of the old charge l3, with a boundary of impurities 12 between this charge and a previous charge 15. After withdrawal of the ram, charging-ofthe press cylinder H with a new charge iii of molten lead and extrusion of a substantial portion of this new charge after it has solidified, the layer of impurities l2 will be seen to have flowed along with the portion of new charge l6 which has been extruded, as shown in Fig. 3. As a result, the impurities l2 are occluded betweenold charge [3 and new charge l6 near the upper portion of the cable somewhat as shown in Fig. '4. At a later stage in the extrusion of new charge I 6, as shown in Fig. 5, the new charge i6 comprises a larger portion of the sheath with the impurities still being occluded between the interface of the old and new charges [3 and [6, respectively, as seen in Fig. 6. It is important to note that the impurities are not segregated in a single portion of the extruded sheath but are distributed with a reasonably uniform pattern throughout the entire length of the sheath. These occlusions are thus a dangerously potential source of failure throughout the entire sheath.

When the molten lead is poured through a spout extension and is thus delivered directly against the surface of the old charge IS, a portion I! of the old charge is melted and is combined with cylinder. As the new charge I B is extruded, these impurities appear as flowlines l8 in the charge as indicated in Fig. 8, thus forming segregations of the impurities which subsequently appear in the extruded sheath as indicated in Fig. 9. The presence and position of the impurities shown in Figs. 1 through 9-have been confirmed by study of extensiveseries of photomicrographs. It is the elimination of the presence of such impurities to which the present invention is directed. Their press before delivering the next charge to the press cylinder.

The cutter shown in Figs. 10 and 11 has been developed as an effective means of loosening and removing these surface impurities. The cutter comprises a disc 20 welded or otherwise secured to the end of a driven shaft 2|. The disc is provided with a radial slot 22 which extends from substantially the center of the disc to its periphery. One side of the slot is beveled as indicated at 23. The lower surface of the disc 20 below this beveled side is undercut as indicated at 24 to accommodate the cutting member 25 provided with a sloping cutting edge 26 which has substantially the same slope as that of the beveled side 23 of the radial slot. Thus, the beveled side of the slot and the sloping cutting edge 26 form a substantially continuous surface extending from the upper surface of the disc to a point extending a relatively short distance below the lower surface of the disc. The cutting member 25 is secured to the disc by suitable means such as screws 21, or the like, with a space left between its sloping cutting edge 28 and the leading edge 28 of the slot.

In order to maintain the spacing of the disc within the extrusion press cylinder ll so as to avoid any possibility of scoring the inner walls of the cylinder, a plurality of spacing elements 30 may advantageously be welded or otherwise secured in appropriate slots 3| spaced around the periphery of the disc 20. These spacing elements project only a short distance beyond the periphcry of the disc, and their lower projecting surface slopes upwardly to clear the surface 32 of the lead being cut. The disc is rotated by any suitable driving means engaging the upper end of the drive shaft 2|.

The cutter is used as follows in accordance with the invention. After the ram of the extrusion press has reached the end of its stroke, it is withdrawn from the press cylinder. The cutter is inserted within the cylinder l I and lowered into contact with the surface of the charge of lead in the bottom of the cylinder, The drive shaft 2| is then rotated by any suitable driving means so as to rotate the disc 20. As the disc rotates, the lowermost point of the sloping cutting edge 28 cuts into the surface of the lead. The dross and oxidized lead which is thus loosened passes upwardly through the slot 22 onto the upper surface of the disc, usually in the form of a single strip or chip. A single revolution of the cutter may remove most or all of the surface impurities, although it is presently preferred to make several revolutions of the cutter toinsure complete removal of these impurities.

The cutter of the invention is adapted to remove the surface impurities from the lead remaining in the press suiiiciently rapidly to avoid the formation of oxides on the freshly cut surface of the lead. This is particularly true of leads of at least the commercial grade of purity. Leads of greater purity exhibit in general a greater resistance to oxidation so that the higher the purity of the lead the lesser will be its tendency to oxidize. Conditions may warrant, however, the greatest precautions in preventing the possible formation of oxides on the freshly cut surface of the lead, and in such a case the loosening and removal of the impurities from the surface of the lead may be carried out with advantage while maintaining a non-oxidizing atmosphere in the press cylinder by any suitable means. For example, carbon dioxide may be delivered to the press cylinder through a flexible hose extending.

down into the cylinder; The carbon dioxide, being heavier than air, readily displaces the air in the cylinder and is thus used with particular advantage. However, other non-oxidizing atmospheres may be used, whether lighter than air or not and whether merely inert or reducing in nature such, for example, as nitrogen, carbon monoxide, and the like.

After the surfaceimpurities have been loosened by rotation of the cutter disc, the shaft 2| is raised to lift the disc out of the cylinder and with it the loosened surface of the lead charge. Any loosened particles not removed with the disc may be removed if necessary by suction or other means before introducing the succeeding charge I 4 of lead. The freshcharge of molten lead is poured into the cylinder either from the conventional spout of a lead melting kettle or through an extension on such a spout extending down into the lowermostportion of the cylinder. Thisstep may al-so'be carried out advantageously whilemaintaining a; non-oxidizing atmosphere within *Insteadoffcharsing the lead in the molten 'fo'rm as"previously-described, it may be charged 4 "ill; thegsolid form as is" now" common practice. solid chargdcomprising a slug of lead cast to conform closely to the 1 internal diameter" of the press cylindenis then advantageously pro- 1 vided at one end with a freshlycut surface of suitable shape to insure a substantially non'-oxivdized surface if such 'a surface .is; not already present, and the slug "is then lowered into the presscylinder with this freshly cut surface ad'-- iacent the freshly cut surface of thecharge re-L maining in the press from which substantially all of the loosened particles have been removed as I previously described. By 'charging this slug to.

the cylinder promptlyafter removing the loosened surface material, appreciable re-oxidation of the surfacejof the hotleadcharge remaining in the press may beavoided without maintaining a non-oxidizing atmosphere in'the press cylin-x However," tlieguse of such .a non-oxidizing J atmosphere may bedesirable under the conditions. r set forth in conjunction with. the previous aescription of charging the lead i'nmolten form. The press ram is then moved down into-the cyl inder, the force of ltheramcausing the two; clean surfaces oflead towels! or fuse togethersoas .to provide continuity of quality-between vthe'two charges characteristic of the invention. Pro- 1 vision of the slug of solid lead with a spherical or conicalor similarly shaped lower surface fader.

cilitates bonding of thenew charge to that'pres entln the press cylinder-by facilitating thejflow I of new charge into intimate bonding contact with- .theclean surface of-the previous charge without fentrapmentoi'air.-"

Although the method of the invention has been described inconnectionwlth the-cuttcr-described herein, the method may be carried outwith other 6-0 Number means for mechanically loosening and removing the surface impurities. For example, rotary end cutters, rotaryand scrapers having negative 'rakes, milling cutters or scrapera sanding devices, sand blasters, and other devices adapted to remove mechanically the surface of the lead remaining in the press cylinder may be used in accordance with the invention. Such devices may be combined with appropriate means for 10 receiving and collecting the surface material as it is loosened so that the loosened material may be removed along with the device itself as the latteris withdrawn from the press cylinder. How ever, the use of any surface-loosening device which is not capable of removing the loosened material will require the use of a suction device or other mechanical means for removing the loosened material from the cylinder before a fresh batch of lead is charged.

The method of charging lead into an extrusion press in accordance with the invention has been tested by extruding fifteen molten charges in this manner into lengths of empty lead sheath or Z pipe. plied'to each full length of sheath until failure.

The tests have shown that the impurities have Internal hydraulic pressure was then apbeen substantially completely eliminated and that the pipes were substantially perfect, failure in each case occurring naturally after a relatively J long'life at high pressure. 'The failures showed no signs of undesirable flow lines, nolack'of uniform bonding, and no oxide or other foreign inclusions. 1

I claim-2 1.- The method of charging-lead toan extrusion press which comprises cutting and removing substantially the entire upper end surface of the lead'remaining from a previous charge to remove dross andoxidized lead therefrom-and to provide 40 a clean surface, and introducing into the press in contact with said clean surface anew charge .of lead for further extruding operations.

2. The method of charging lead to an extrusion press "which comprises providing a non-oxidizing atmosphere over the lead remaining in the press I from. a previous charge, cutting and removing s'ubstantiallythe entire upper-end surface of said lead to remove drossjandfoxidized lead therefrom and to provide ablean surface, and introducingto into-the press in contact with said clean surface a new, charge of lead for furtherextruding opera- I I w 6.x FR .1 5. i REFERENCES CITED following references are record in the file of this patent:

. tions,

' s'rarns PATENTS Date Name n ,879,861 Bennett Sept. 27, 1932 1,9 7 2, 7-10 Jacobson Sept. 4, 1934 2,049,931- Alden et al.- Aug. 4, 1936 j 2,185,487; Weddell Jan. 2, 1 949 ,F OREIGNPA'1@8T8 Number. 1 Country Date 570,282 Germany Feb. 13, 1933 572,354 

